In the diagnosis of many conditions, for example heart disease, it is useful to recognize perturbations in intravascular fluid volume. For example, an increase in intravascular volume may indicate decompensated heart failure. A decrease in intravascular volume can indicate dehydration. Both of these conditions are potentially dangerous. In some cases, these conditions are life-threatening.
An important parameter for the recognition and quantification of such perturbations is the left-ventricular filling pressure. This pressure is best quantified by measurement of left-ventricular end-diastolic pressure, “LVEDP.”
A particularly accurate way to measure the LVEDP is to catheterize the left ventricle of the heart. This provides a direct measurement of the LVEDP. Because of its accuracy, this method is often said to provide the “gold standard” for LVEDP measurement.
However, catheterizing the left ventricle is highly invasive and dangerous, with complications that include stroke and death. Consequently, it is undesirable as a routine diagnostic test. Because of the danger inherent in catheterizing the left ventricle, a direct measurement of LVEDP is generally available only when a catheter has been placed in a patient's aorta for some other reason, for example during diagnostic coronary angiography to document the presence and severity of coronary artery disease. In this setting, LVEDP is measured by moving the coronary angiography catheter tip below the coronary artery and across the aortic valve so that the tip of the catheter is in the patient's left ventricle. Once the catheter tip is in the left ventricle, LVEDP can be measured directly.
A more common approach is to indirectly measure LVEDP. This is done by passing a pulmonary-artery catheter through the right ventricle of the heart and into the lungs, where it is positioned to measure the pressure in the capillary bed of the lungs. This pressure, which is referred to as the “pulmonary capillary wedge pressure” (PCWP), provides a clinically useful estimate of the filling pressure of the left ventricle of the heart. While the insertion of a pulmonary artery catheter comes with its own set of complications, it is much less dangerous than catheterizing the left ventricle of the heart.